This invention relates to a production method of developer components such as toner particles and carrier particles.
With respect to a developer for developing electrostatic latent images, a single-component developer of (non-)magnetic toner particles or a two-component developer containing toner particles and carrier particles is widely used in response to developing system.
There are proposed many kinds of composite toner particles for one-component developer or two-component developer because various physical properties, such as coloring properties, fixing properties, chargeability, fluidity and the like, are requested generally.
The composite toner particle is constituted of plural layers each of which has specified properties, such as fixing properties, chargeability and the like. As chargeability of toner for example, depends much on physical properties of the surface of toner, a charge controlling agent need not to be contained inside the toner but on the surface of the toner to achieve the object of the addition of the charge controlling agent. Further, a layer of resin particles is often formed on the surface of toner.
In conventional formation of the composite toner particles, fine particles for surface modification, such as a charge controlling agent, resin particles and the like, are adhered to the surface of core particles by aid of van der Waals force, electrostatic force and then given impact force in high speed current to be settled thereon.
However, as the fine particles are, in a sense, hammered into the core particle by impact force to be merely settled on the surface of the core particle, they are apt to separate from the core particle when mixed and stirred with carrier particles for frictional electrification. The separated fine particles scatter inside a copy machine and have many harmful influences, such as pollution, fogs on copied images and the like. The separation of the fine particles causes the deterioration of uniformity of many characteristics of toner.
As the surface of core particle is uneven, some fine particles adhere to hollow portions. Such particles are liable to be not settled even when treated by impact force in high-speed current. Therefore, it is difficult to modify the surface of toner uniformly This phenomenon become more remarkable as the ratio of fine particles increases.
Toner particles inferior in uniformity of the surface, for example, are electrically charged oppositely or not charged sufficiently, and bring about problems, such as scattering in a copy machine, pollution and the like.
With respect to carrier utilized in a two component developer, many kinds of composite carriers are proposed. The many problem as above mentioned also the case with the carriers.
In conventional techniques, many kinds of composite toners are proposed (for example, Japanese Patent Laid-Open Sho 62-209541) in which many kinds of fine particles (for example, a charge controlling agent) having a one fifth or less size of core particle are adhered to the surface of resinous core particle and then the fine particles are settled by shearing force. However, a heat treatment is not carried out to modify the surface uniformly as will be disclosed by the present application below. Japanese Patent Laid-Open Sho 59-37553 discloses that binder resin and fine particles are mixed to be subjected to heat-treatment in hot current at 200.degree.-600.degree. C. However, as the binder resin and the fine particles are merely mixed, the fine particles do not adhere to the binding resin uniformly. Even if such a product is treated in hot-current, the fine particles can not be fixed uniformly. In a conventional method, when such a mixture as described above is treated in hot current, binder resin particles themselves aggregate and fuse. In particular, it is almost impossible that fine resin particles are treated to form a layer.